Mechanical stability can be checked by computing the force constants (or the Hessian matrix of the energy second derivatives). If it is positive definite then your molecule is stable, meaning it will not deform as it is at its energy minimum.

Chemical stability maybe checked by calculating the HOMO-LUMO gap. An open-shell system would be unstable and can chemically react very easily, while a large gap molecule would be inert (such is the case of rare gas atoms where the gap is large), because it will not easily hybridize with the atom or molecule that is approaching it.

This compound is called o-aminobenzonitrile. It is NOT inert but it has 2 groups that counter each other (-CN is deactivating & meta- directing) and (-NH2 is activating & ortho-, para-directing). Directing means that the incoming group or atom  (G) in electrophilic aromatic substitution (E.A.S) will go to the position(s) specified as the attached equation shows

Thanks for the answering, but whatever you are telling to me thats I know. Whereas I asked in a different way and ya it is inert/ less reactive for reactions like converting CN to tetrazole or converting NH2 to some other functionalties or substituting NH2.

But thanks once again for the answering and my question is in regard to know about the computational chemistry approach or method where I can prove it, as a tough substrate for any reaction.

Your comment clarified the picture. We used to have an experiment in Practical Organic Chemistry (II) in which the students prepare  p-bromoaniline. If one starts with aniline, polysubstitution occurs because    - NH2 is powerful activating group , so aniline is converted first to acetanilide by acetic anhydride (i.e.  -NH2 becomes   -NHCOCH3) then Br2 (in glacial acetic acid) is added to give p-bromoacetanilide after which simple acidic hydrolysis is applied to give p-bromoaniline. The group -NH2 on aromatic ring cannot be substituted neither by SN1 nor by SN2 . When one wants to convert -CN group to tetrazole, this involves reduction (since H is added) but in a reduction -CN  preferrably goes to    -CH2NH2.

In short, this compound has contradictory effects but it is NOT inert. What is most stable is the benzene ring itself but the attached groups can undergo changes except substitution by other groups (which needs drastic conditions).

Thanks @ Dr Nizar for your valuable reply and understanding the problem. But I need a computational software  or method which can evaluate this hypothesis that it is quite stable because of the resonance between the CN and NH2 groups and therefore decreasing reactivity  for certain reactions.

Since you have cyano derivatives you probably need to deal with multiconfigurational problems and hence you require a multiple reference wave function. My suggestion is the approach of the CASSCF/CASPT2 which implies that your CASPT2 energies are computed at CASSCF optimized geometries. To do so there are different softwares, MOLCAS is the most applicable software to run CASPT2 calculations. I hope this helps you to peruse your system.

Hi Pooria !! Thanks for the your valuable concern. But I think MOLCAS is paid software and if i get its evaluation trial version even-though don't get the intellectual propriety rights. So please tell me any other software which can be free for use.

Hi Arvind ! Hmm, That's right. I didn't think of that. Then I suppose you can try MOLPRO, which I'm afraid it is not open source as well. But in case of multiconfigurational problems, surely Gaussian (Any Edition)  is the worst one. Then try to look for multiconfigurational codes, another method can be multionfigurational coupled-cluster approaches. This "paid software stuff" is the most stupid idea in science . 

If you want to try multiconfigurational calculations, different flavors of GAMESS (e.g. http://www.msg.ameslab.gov/gamess/) and Firefly (http://classic.chem.msu.su/gran/gamess/index.html) and  Orca (http://cec.mpg.de/forum/) (all are free software) can all be used.

Just a remark:

- Multyconfigurational calculations are pretty involved ones, so if you are beginner in quantum chemistry, maybe it is not the smartest idea to start with those. 

If you new to the field, I think you profit much more from (significantly) lower level of calculations, DFTs or even semi-empiricals which happen to be implemented in the aforementioned software.

using Gaussian software with a high level methods such as MP2/Aug-cc-pvtz or M062x/Aug-cc-pvtz or ccsd/aug-cc-pvtz for geometry optization can help you to solve your problem

Thanks Gergely and Mohd. Reza for your valuable reply. But I am new to this quantum calculation. can you tell me some easy method to just support my hypothesis.

Mechanical stability can be checked by computing the force constants (or the Hessian matrix of the energy second derivatives). If it is positive definite then your molecule is stable, meaning it will not deform as it is at its energy minimum.

Chemical stability maybe checked by calculating the HOMO-LUMO gap. An open-shell system would be unstable and can chemically react very easily, while a large gap molecule would be inert (such is the case of rare gas atoms where the gap is large), because it will not easily hybridize with the atom or molecule that is approaching it.

Here is the figure that i am attaching:

Figure 1: indicating simple NH2 conversion or reaction to form product in 4-5 hr

Figure 2: If cyano is adjacent to the NH2, then drastically time gets increased (24-36 hrs)

Figure 3: It can be resonance. 

Now can i have some easy calculations for these reactions to support resonance effect in making the reactant so much stable.

FIGURE ATTACHED!!

Dear Gergely Juhasz,

The software links you have provided were not working. How to get them kindly send me other different links to download.

waiting for your possible reply.......

Hi Arvind,

Based on your attached figures, I would suggest you to run two separate geometry optimization jobs. One for the Aniline and the other for the ortho-amninobenzonitrile. After you obtained the optimized geometries you can run further analysis on your molecules and get their atomic charges, electrostatic potential maps(ESP), natural bond orbital analysis(NBO), and HOMO-LUMO gap, .... to compare. Hopefully, you can interpret these differences and find a good explanation for the behavior of your molecules.

You already received good suggestions for free softwares in previous comments.

Bests

Fatemeh

to check the stability of your compound, I think you should get initial structure using a poor method such as INDO optimization, after that take the optimized geometry and reoptimized using DFT method with frequency test to be sure that the structure is minimum. I think there is intramolecular forces between CN and NH2 substituents which makes the optimization is hard, I am sure the suggested procedure will work

Also if the optimization is not converging, give it some temperature (fractional electronic occupations, also called smearing). That might alleviate the lack of convergence issue if it is due to degeneracies or partially filled HOMO states.